In recent years, a technology called OpenFlow has been proposed (refer to Non-Patent Literatures 1 and 2). OpenFlow treats communication as an end-to-end flow and performs path control, failure recovery, load balancing, and optimization for each flow. An OpenFlow switch, specified in Non-Patent Literature 2, comprises a secure channel for communicating with an OpenFlow controller and operates according to a flow table suitably appended or rewritten by the OpenFlow controller. In the flow table, a set of matching conditions (Match Fields) matching a packet header, flow statistics (Counters), and Instructions defining the content of processing is defined for each flow (refer to the section of “4.1 Flow Table” in Non-Patent Literature 2).
For instance, upon receiving a packet, the OpenFlow switch searches for an entry having a matching condition (refer to “4.3 Match Fields” in Non-Patent Literature 2) that matches the header information of the received packet in the flow table. When an entry matching the received packet is found as a result of the search, the OpenFlow switch updates the flow statistics (Counters) and performs the processing content (packet transmission from a designated port, flooding, discard, etc.) written in the instruction field of the entry on the received packet. On the other hand, when no entry matching the received packet is found as a result of the search, the OpenFlow switch requests the OpenFlow controller to set the entry via the secure channel, transmitting a request (Packet-In message) to transmit control information for processing the received packet. The OpenFlow switch receives a flow entry that defines processing contents and updates the flow table. As described, the OpenFlow switch forwards packets using entries stored in the flow table as control information.
[Non-Patent Literature 1]
    Nick McKeown, et. al. “OpenFlow: Enabling Innovation in Campus Networks,” [online], [searched on Oct. 4, 2012], the Internet <URL: http://www.openflow.org/documents/openflow-wp-latest.pdf>[Non-Patent Literature 2]    “OpenFlow Switch Specification” Version 1.1.0 Implemented (Wire Protocol 0x02), [online], [searched on Oct. 4, 2012], the Internet <URL: http://www.openflow.org/documents/openflow-spec-v1.1.0.pdf >